The value of polyculturing trochus (Trochus niloticus) or a similar herbivorous species of archeogastropod along with the blacklip pearl oyster spat/juveniles. 

 

Since the start of the mass culture of giant clams in the mid-1980s, the idea of polyculture with trochus was tested in Palau, MMDC, North Queensland - James Cook University's Orpheus  Island Research Station, Solomon Islands, ICLARM. 

 

The result was good, as long as trochus juveniles were still small when the clam juveniles were small (Trochus spawning 1-2 weeks before or about the same time as the clams].

 

This avoided any problem of trochus which were too large for the clam juveniles running over them and damaging or killing them with their shell or radular teeth scraping algae off the substrate. During the Asian Development Bank project to assist the Blacklip Pearl Oyster project in Penrhyn, Cook Islands, trochus were spawned and added to land nursery raceways with spat and juvenile blacklip pearl oysters.

 

The result was positive in that the trochus helped to curtail growth of the filamentous algae growing on the sides of the raceway and on the blacklip spat/juveniles themselves spawning and larval rearing of trochus and other similar archeogastropods is relatively easy in comparison with pearl oysters.

 

Larvae are lecithotrophic (have yolk reserves so no larval feeding necessary) and the larval period is only about 3 days before settlement. The following information gives a background on trochus  culture to date.

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The first research on the biology of trochus was done in Palau by Japanese biologists in the 1930s and early 1940s, and also by an Australian marine biologist, F.W. Moorehouse (1932) on the Great Barrier Reef.  The documentation on the spawning of trochus and rearing of the larvae to young juveniles was first accomplished in the late 1970s and early 1980s in Palau by researchers such as Ann Hillman and Gerald Heslinga at the MMDC (Micronesian Mariculture Demonstration Centre).

 

Gerald Heslinga and Rick Braley successfully spawned broodstock and reared large numbers of larvae to settlement in two 100-tonne concrete tanks at the MMDC in mid-1979. This was the stimulus for MMDC to become committed to improving the culture of trochus during the 1980s.

 

During the 1980s, Mr. G. Heslinga reared the larvae and juveniles of Trochus niloticus in concrete raceway tanks [8m x 1.5m x 1m] and the juveniles were polycultured  with juvenile giant clams (family Tridacnidae). The trochus were spawned about 3 weeks – 1 month before the spawning of the clams, so that when the juvenile trochus were about 3-4 monts of age they could be collected and added to the tanks with 90 day old juvenile clams. 

 

The juvenile trochus would then eat filamentous algae and diatoms from the bottom of the clam tank and also clean off algae which would grow on the clam shells or over them. The MMDC regularly produced 1000s of trochus juveniles in each spawning throughout the year. These were almost all used in the above-mentioned polyculture system.

 

During the ACIAR-James Cook University (JCU) International giant clam project, Rick Braley and other project staff cultured trochus juveniles similar to the protocol in Palau for use with the giant clam juveniles. After that project ended in 1992 the trochus research work at JCU continued with the then PhD-candidate researcher, Laura Castell. Her work involved small-scale rearing in Australia with re-seeding experiments in both Australia and Vanuatu. 

 

Results from the experiments of releasing cultured juvenile Trochus niloticus onto coral reefs indicated that after 3 days, 20-40% of the juveniles are missing. Predation was deemed to be the main cause of mortality. Seeding densities used were from 5-30 juveniles/m2. She suggested that seeding densities of not greater than 10 juveniles/m2 are advisable. 

 

The work in Australia has shown that juveniles larger than 24mm shell diameter survive better than smaller sizes because predation by Portunid crabs and stomatopods is minimised above 24mm shell diameter.

 

Another ACIAR-funded project was based out of Northern Territory University (NTU), Darwin and involved two Universities and a government Marine Research Facility in eastern Indonesia, and the Fisheries Department in Vanuatu. One of the products of the project was ACIAR Proceedings No. 79 (published 1997) entitled Trochus:  Status, Hatchery Practice and Nutrition. A recirculation system was developed at NTU which involved the spawning, larval culture and nursery culture of juveniles.

 

In regards to private ventures involved with the aquaculture of trochus, there have not been many yet, because the trochus resource is still available in the sea for collection. However, one Chinese-Indonesian businessman took the step to make the aquaculture of trochus commercial.

 

Dr Richard Braley prepared plans for a hatchery and nursery facility for at a pristine site near to one of his pearl oyster hatcheries and growout farms in western Ceram Island [Maluku, eastern Indonesia].

 

The plans were made in 1995 and work began on the facility by latter 1995, being essentially completed by May 1996 when Dr Braley carried out training with the hatchery technicians and conducted the first spawning/larval rearing for the facility. 

 

The owner's goal was to be able to culture enough trochus shell that he could harvest 100 tonnes of shell per year. The hatchery/nursery designed included 10 concrete raceways (8m x 2m x 1m = ~ 15 tonnes seawater/raceway when filled), 12 concrete tanks (3m x 1.5m x 0.8m = ~3.4 tonne seawater/tank when filled), and other smaller tanks, a dry lab, and an algal culture lab.  

 

Although broodstock were not very common locally, the initial large spawning was successful and Dr Braley was informed after 12 months that there were still ~1,000,000 trochus juveniles in the large raceway tanks from the initial spawning and settlement (about 40% survival). These averaged about 20 mm shell base diameter, though many were larger than 25mm.  

 

As this was the first commercial trial, future details of the culture protocol can be improved to produce more optimal faster growth and higher survival. Dr Braley advised the owner that they should try growing out juveniles in concrete intertidal ponds, in plastic-lined non-tidal ponds, and in intermediate hanging basket culture. He is not aware if they have trialed these methods of growing juveniles but they had ideal conditions at his pearl oyster farm because workers, boats, rafts, longlines, etc. were all available at the site